Used to study the movement of ocean currents, underwater sound beacons emit a specific tone that can be recorded and timed by neutrally buoyant floats. This example was recorded by the autonomous hydrophone array in the Gulf of Alaska. The signal ramps up to about 270Hz and lasts for about 3 minutes.

Click on spectrogram for full-sized image.

1,697K wav file(The recorded signal has been sped up 2 times)